See if this car has all the permits. If it is a one-time payment, you must have all the warrants. If you pay by installment, the ownership belongs to the bank, because if you borrow money from the bank to buy a car, you have to mortgage the ownership of the car to the bank.
The bank promises to return the ownership to the customer after paying the principal and interest, and auction the car to compensate for the loan in case of default. So you can ask the owner to show all the warrants. The same is true for mortgage loans to buy a house.
If you want to check whether there is a loan for the car, you can check whether the words mortgage car are printed on the vehicle registration certificate. If there is a mortgage car, prove that your car is a loan car.
Or you can check with the vehicle management office and the insurance company. When the loan car is mortgaged, the vehicle management office will put it on record. Check with the insurance company who is the insurance beneficiary. If the beneficiary is a lending institution, prove that the car is a loan car.